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vCPU assignment/calculating

Thorsten Bolz


Good morning together,


i think i not really understand the calculating of vCPU for my XenApp7 workers...

we have a dual socket Server with 8 Cores per Socket (XeonSilver 4110) and Hyperthreading active.

We want to run 4 Workers on each Xen 8 Hypervisor.


My Calculating:  2 Sockets with 8 Cores= 16 and Hyperthreading active=32   2Numa=16 and a overcomit ratio 2 = 32vCpu


i assign 1 Socket with 8 Cores to every Worker


Is that the correct way?




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See also perhaps the article https://www.mycugc.org/blogs/tobias-kreidl/2019/04/30/a-tale-of-two-servers-part-3

as well as its previous parts 1 and 2 for some hopefully helpful information. Sorry, I thought I posted this the other day and I guess it didn't take initially for some reason.


The assignment of vGPUs to cores or sockets needs to take NUMA into account, as well as licensing restrictions whih limit options on some Widows opeating systems.



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Hi Thorsten


First off, it's best not to include the hyper-threads in your calculation, because these only give you about a 20% performance increase. Consider these your "spare" capacity, in case you have usage spikes

Just to be sure, you'll be running XenApp (Citrix Virtual Apps)?

Dimensioning your environment needs, all starts with what kind of workload you will have running, or in other words, what kind of users are going to be on the VDI's, and what kind of applications are they going to be running?
You can probably fit them in these categories:

  • Task workers; using a single, low-demanding (single threaded) application
    For instance, callcenter operators
  • Knowledge workers; using multiple, low-demanding (single threaded) applications
    Like people using the Office Suite, and other, "administrative" applications
  • Power workers; using multiple, high-demanding (sometimes multi threaded) applications
    Like Designers (f.i. using Adobe Suite) or CAD workers (f.i. using AutoDesk applications)

Which category would your users fit into?


Additionally, for power Workers, you'd probably also need (v)GPU and then you'd ideally be using XenDesktop (Citrix Virtual Desktops).






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15 minutes ago, Martijn Kools said:

Hi Thorsten,


It's better to assign 8 sockets with 1 core each rather than the other way around, if your OS allows it (2008 R2/2012R2 might not, 2016 does).

Normally you would assign numa or half numa to each VM so yeah I would assign 8 sockets to each VM.








Interesting @Martijn Kools, what's your reason behind that?

By the way, Thorsten is talking about XenApp, so the concept of cores/sockets per VM doesn't make any sense there. Although I see the confusion, when talking about cores per worker.




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Hi Thorsten,


With XenApp, the concept of vCPUs per worker is gone - even when using a published desktop - because you are still sharing all resources of the machine amongst the users.

Unless you are actually running multiple virtual machines on that physical host (with the amount of vCPUs you mentioned), then install the Citrix VDA on there, to use them as XenApp hosts, and run a published desktop per virtual machine? But that wouldn't make sense, you would be better off doing actual XenDesktop (Citrix Virtual Desktops) on those virtual machines.


Anyway, a knowledge worker will probably not need more than 2 vCPUs, and would generally not be using more than 1 GHz at any given time, so depending on the clock speed of the CPUs in that system (I'm going to assume it is around 3 GHz), you could run about 3 users per physical core, so in total 48 users. But most likely, memory will be the more limiting factor.
A knowledge worker probably won't use more than 4 GB, so you can base your calculation off that.


Hope that makes sense.





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